Since glycine has such a small
side chain, it can fit into many places where no other
amino acid can. For example, only glycine can be the
internal amino acid of a collagen helix.

Glycine is very evolutionarily
stable at certain positions of some proteins (for example,
in cytochrome c, myoglobin, and
hemoglobin), because mutations
that change it to an amino acid with a larger side
chain could break the protein's structure.

Most proteins contain only small
quantities of glycine. A notable exception is collagen,
which is about one-third glycine.

According to computer simulations
and lab-based experiments, glycine was probably formed
when ices containing simple organic molecules were
exposed to ultraviolet light.

Before glycine, more than 130
simpler molecules were found in deep
space, including sugars and ethanol. But amino acids, sometimes called
building blocks of life, are a much more interesting
find.

This does not prove that life
exists outside Earth, but certainly make that possibility
more likely, proving that amino acids exists in outer
space. This also indirectly supports the idea of Panspermia, saying that life
was brought to Earth from space.

Physiological function

Glycine is an inhibitory neurotransmitter in the
central nervous system, especially in the spinal cord. When glycine
receptors are activated, chloride ions enter the neuron
and the cell undergoes a hyperpolarization. Thus the
cell tends to be in an inhibited state. Strychnine,
a drug that cause convulsions, acts by blocking these
glycine receptors.